Bulletin Volume 532-538 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1913 Excerpt: ...slope glaciers is the greater area of their accumulating grounds. On the south slope the average distance from the crest line to the base of the main range is more than 25 miles, whereas on the north it is only half this Brooks, A. H., op. ctt., p. 12S. 'Capps, S. R., The Bonnifield region, Alaska: Bull. U. S. Geol. Survey, No. S01,1912, pp. 36-38. distance. The area of accumulation of those glaciers which he on the north slope is therefore much more restricted and the glaciers are correspondingly smaller. The erosive action of the glacial ice in the mountain valleys of the Yentna region was very great, as is shown by the perfectly developed cirques and straight, broad, U-shaped valleys. Kahiltna Valley at the lower end of the glacier lies about 1,000 feet below the level of the plateau on either side of it, and glacial scour was certainly the cause of a considerable portion of this deepening, though perhaps not of all. Yentna Valley also shows the effects of profound erosion, as does the Tokichitna Valley. In the areas between these great troughs there is evidence that glacial scour was much less severe. The broad basin between Tokichitna and Kahiltna rivers, occupied in part by Cache Creek, is floored with soft, easily eroded deposits, as is also the plateau between Yenlo Hills and Chelantna Lake. These areas were glacier covered and may have been stripped of some material, but by virtue of their protected positions escaped such vigorous grinding as that to which the main valleys were subjected. It is doubtful if the glacier removed any great quantity of sediments in the lowland or scoured the hard bedrock except at those places where hills of hard rock projected through the Eocene sediments. In the lowland in many places glacial till and stream gravels o...